1. Field of the Invention
The present invention relates generally to a real-time fluid monitoring and concentration control system for maintaining concentration of one or more selected species in multicomponent fluids at a desired level, e.g., in a range defining effective or optimal operation.
2. Description of the Related Art
In the field of semiconductor manufacturing, a number of multicomponent fluids are employed to carry out process operations, including etching, chemical mechanical planarization (CMP), photolithography, chemical vapor deposition, spin-on coatings application, supercritical fluids cleaning operations, wafer solvent drying operations, to name a few.
In many of these process steps, the relative concentrations or proportions of various components in the multicomponent process fluid must be maintained at a predetermined value or within a selected range, in order to achieve satisfactory results and avoid the necessity of rework or discarding of defective semiconductor device structures, including finished devices as well as precursor structures thereof.
By way of specific example, in semiconductor manufacturing operations of photolithography and etch processes, various solvents are employed for photoresist and post-etch residue removal.
Photoresist compositions are solvent-based, light-sensitive solutions, which are uniformly applied to a semiconductor wafer and then processed to leave a selected pattern of cured photoresist on the wafer after development. Etching then is carried out, wherein reactive gases or liquids are used to remove undesired material from the wafer surface, in the areas where the material is not protected by the cured photoresist.
During etching, various chemical complexes are formed or remain on horizontal and vertical surfaces of the structures being delineated. At the completion of the etch process, these complexes are no longer necessary and need to be removed, together with any remaining cured or uncured photoresist. This is typically accomplished using a mixture of fluids in gaseous, liquid or supercritical state or a combination thereof. Solvent mixtures used for the liquid removal of the cured photoresist and post-etch residues from the wafer include both acidic as well as basic solvent compositions.
The ability of the solvent chemistry to remove the cured photoresist and post-etch residues is strongly dependent on the ratios of its components. In addition, many solvent components require an elevated operating temperature to be effective. However, in solvent systems where water is a component, heating the solvent causes the water to evaporate. If not enough water is present in these solvent systems, then the solvent can become ineffective. Conversely, if too much water is present, damage may occur to exposed surfaces on the wafer. Therefore, an out-of-specification solvent mixture can result in severe damage to the wafers and/or a failure to remove undesired materials such as the photoresist or etch-generated residues.
In addition to process instability, significant costs can be incurred due to the limited lifetime of these solvent mixtures. These can variously include: costs of the chemicals; costs associated with equipment downtime reducing the production efficiency of the manufacturing facility; costs associated with an incremental and/or catastrophic yield loss due to device parametric failures of defective wafers resulting from use of out-of-specification chemicals, and disposal costs of the high volumes of required chemicals.
The problems attendant the use of out-of-specification multicomponent solvent compositions in removal of photoresist and post-etch residues are illustrative of the difficulties encountered in many industrial processes in which compositional uniformity of a multicomponent fluid composition is critical to meeting process objectives and commercial viability.
The foregoing provides a background to the advance of the present invention, as described more fully hereinafter.